The Defensive (aka "Nose") Tackle in a 3-4 lines up over the offensive center. His responsibilities include:

1) Stop the run, particularly in the middle of the field
2) Maintain position with a low center of gravity - tie up at least 2 offensive linemen, allowing linebackers to pursue the flow of play
3)Provide interior pass rush, pushing and collapsing the pocket

This diagram shows the Nose Tackle in a standard 3-4 alignment. His responsibilities are based on the following factors:

A. Prevailing defensive philosophy: In a "read and react" 3-4, the defensive line controls the offensive line to allow the LBs to flow to the ball. In "attack and penetrate", the defensive line takes more of a 1-gap approach and the LBs have more gap responsibilities.

B. Opponent's offensive philosophy: On running plays the Nose Tacvkle has the responsibility of clogging the middle, with support from the linebackers and strong safety. Responsibilities in the passing game are 1) collapsing the pocket, 2) providing an interior pass rush and 3) increasing length (hands and arms up) to limit the opposing QB's vision of passing lanes.